The precise mechanism of cell mediated immunity is still not clear. However, delayed hypersensitivity is believed to play an important role in clearing viral infections since it has been shown that intracellular replication and cell to cell transfer of virus can occur in presence of high levels of antibody. It has been suggested that SSPE, a chronic measles virus disease of the CNS, is due to specific deficiency in the cellular immune system. This project proposes to develop an in vitro assay system to investigate the role of cell mediated immunity in the immunopathogenesis of SSPE.